Typically, gas turbine engines are formed from a combustor positioned upstream from a turbine blade assembly. The compressor is formed from a plurality of compressor blade stages coupled to discs that are capable of rotating about a longitudinal axis. Each compressor blade stage is formed from a plurality of blades extending radially about the circumference of the disc.
The tips of the compressor blades are located in close proximity to an inner surface of the compressor casing of the turbine engine. There typically exists a gap between the blade tips and the compressor casing of the turbine engine so that the blades may rotate without striking the compressor casing. Likewise, for nonshrouded compressor vanes, there typically exists a gap between the vane tips and an internal rotatable compressor blade and disc assembly so that the rotatable compressor blade and disc assembly may rotate without the compressor vanes contacting the rotatable compressor blade and disc assembly. During operation, gases pass the compressor blades and vanes and compress to high temperature and pressure. These gases also heat the compressor casing, blades, vanes and discs causing each to expand due to thermal expansion. After the turbine engine has been operating at full load conditions for a period of time, the components reach a maximum operating condition at which maximum thermal expansion occurs. In this state, it is desirable that the gap between the blade tips and the compressor casing of the turbine engine and the gap between the compressor vanes and rotatable compressor blade and disc assembly be as small as possible to limit leakage past the tips of the airfoils.
However, reducing the gap cannot be accomplished by simply positioning the components so that the gap is minimal under full load conditions because the configuration of the components forming the gap must account for warm restart conditions in which the compressor casing and the compressor vane carriers, having less mass than the compressor blade and disc assembly, cools faster than the compressor blade and disc assembly. During a warm restart, the discs expand due to centrifugal forces and the clearances tighten before the casing begins to heat up and expand. Therefore, unless the components have been positioned so that a sufficient gap has been established between the compressor blades and the compressor casing and between the compressor vanes and the rotatable compressor blade and disc assembly under operating conditions, the compressor airfoils may strike the compressor casing or the rotatable compressor blade and disc assembly because the diameter of components forming the compressor casing have not heated up and expanded yet. Collision between the compressor blades and the compressor casing or compressor vanes and the rotatable compressor blade and disc assembly often causes severe airfoil tip rubs and may result in damage. Thus, a need exists for a system for reducing gaps between compressor blade tips and a compressor casing and between compressor vanes and a rotatable compressor blade and disc assembly under full load operating conditions while accounting for necessary clearance under warm startup conditions.